U.S. Pat. No. 6,973,955 B2 issued Dec. 13, 2005 describes a heated trough for the transfer of molten metal. This patent broadly describes a trough comprising an outer shell defined by a bottom wall and two side walls, an insulating layer filling the outer shell and a conductive U-shaped refractory trough body for carrying molten metal, the trough body being embedded in the insulating layer. The device of this patent further includes at least one heating element positioned in the insulating layer, adjacent to but spaced apart from the trough body, to provide an air gap between the heating element and the trough body. The trough is described as being fabricated from a material that is generally highly conductive and resistant to corrosion from molten metal. The only examples of suitable such materials provided in this patent are dense refractories such as silicon carbide and graphite. No definition of the terminology “highly conductive” is presented in this patent. Presumably this term as used in this patent is meant to refer to thermal conductivity since the structure described is utilized to impart heat to molten metal being transferred in the trough. From the literature, it is known that silicon carbide has a thermal conductivity on the order of about 100-300 W/m-K°, and graphite is reported to have a thermal conductivity on the order of above 100 W/m-K° (see www.matweb.com that provides materials properties data of this type). Thus, to the skilled artisan, these materials would be recognized as “highly thermal conductive”.
While the foregoing device provides a useful tool for the maintenance of molten metals temperature during transfer in a trough, it possesses several inherent commercial and technical weaknesses. Most notably, silicon carbide is a very expensive material that, while providing excellent thermal conductivity as noted hereinabove, and very high resistance to erosion and attack by, for example, molten aluminum, it is very difficult to form into shapes such as troughs. As a general observation, a trough fabricated from such a material would be very expensive to produce, and would in all probability not be commercially viable. As to a graphite trough, again while the thermal conductivity of such a device would be very desirable form the point of view of heat transfer, graphite is generally considered much too prone to oxidation and is furthermore generally quite friable (not particularly wear resistant), thus not providing a trough material of suitable commercial value.
Accordingly there exists a continuing need for a device such as that described in U.S. Pat. No. 6,973,955 B2 that is equally useful, but significantly less expensive to produce while providing heat transfer and wear characteristics adequate for use in most metal transfer applications.